This thesis investigates whether an EEG headset can be used to distinguish motor imagery signals in real time for a Brain Computer Interface (BCI).The specific EEG headset used for this project is the gtec Unicorn Hybrid Black. The aim of this subgroup is to stream the data in real time, preprocess the data, and create a training dataset using recordings from subjects. The sample from the EEG headset is streamed to a laptop using a live data streaming framework called Labstreaminglayer. The data is then filtered using frequency filters and ICA to remove noise and artifacts. Finally, ERDS plots are used to check the signal quality of the recordings. Recordings of sufficient quality should have (de)synchronisation peaks after the prompt is displayed. Before the recordings are made, an experimental setup is set up. This includes prompts with four different movements that the subject is asked to imagine. The data is sent to a GUI to be visualized with various graphs. It is also sent to a machine learning model to classify the movements. It was concluded that the subsystem could successfully stream data from the cap, process the data, and verify the quality of the data. Using ERDS plots, it was verified that some, but not all, MI actions are distinguishable for one individual. However, further verification of other individuals is required to conclude whether this is a systematic problem or is due to the individual.

Passivating contacts in the front-rear contacted c-Si solar cells enhances the device performance by quenching the contact recombination and enabling sufficient carrier transport. Tunneling oxide passi- vating contact (TOPCon) which consists of an interfacial oxide and a poly-SiO𝑥 layer is one of the most promising contact techniques in passivating both surfaces of the silicon wafer. However, the full area poly-SiO𝑥 layer is absorptive when it is applied at the front side which has become an efficiency limiting factor. In this project, an advanced local poly-SiO𝑥 passivating contact architecture is proposed and presented. The local poly-SiO𝑥 passivating contacts, so-called “poly-SiO𝑥 finger”, is deposited through a hard mask at predefined locations which will be only placed underneath the metal contacts. The formation of poly-SiO𝑥 finger and its application in the solar cells are discussed.

First, a silicon wafer hard mask is fabricated by a lithography process followed by a KOH wet chemical etch-back process. Specified openings down to 38.7 𝜇m are established which isolate sections of the substrate for the poly-SiO𝑥 finger formation. P+ doped a-SiO𝑥 :H is deposited using PECVD with SiO𝑥 p+ diffused emitter commercial Cz wafers through the hard mask. By investigating the influence of deposition parameters during the PECVD, specifically the power and pressure, decent uniformity of the finger deposition is achieved. An optimized deposition condition of the doped a-SiO𝑥 :H is established for the poly-SiO𝑥 finger formation: an RF power source at 15 Watt, a chamber pressure of 1.5 mbar, and a substrate temperature of 180 °C. A narrow poly-SiO𝑥 finger with a width of 40.0 𝜇m has been demonstrated.

Second, the passivation properties of the symmetrical samples are examined by varying the poly-SiO𝑥 and Al2O3 thickness for the hole carrier selective contacts. A full area p+ TOPCon and Al2O3 symmetric samples were coated on the textured diffused p+ surface with an n-type c-Si substrate to investigate the process parameters on the passivation properties. The optimal 𝑖𝑉𝑜𝑐 of p+ TOPCon samples is 662 𝑚𝑉 and a corresponding 𝐽0 of 156 𝑓 𝐴 𝑐𝑚2 which is obtained with a poly-SiO𝑥 thickness of 50 nm when annealed at 850 °C. The optimal thickness for the Al2O3 passivation layer is achieved by depositing a 20 nm thick layer followed by FGA, with an 𝑖𝑉𝑜𝑐 of 692 𝑚𝑉 and a 𝐽0 of 22.4 𝑓 𝐴/𝑐𝑚2.

Finally, a process flowchart has been created to fabricate c-Si solar cells with the local p+ TOPCon on the front p+ diffused emitter and a full area n+ TOPCon on the rear side. A localized polished area is made by a poly-etch process for the alignment between the substrate and the pattern in the lithography mask. Using the ascertained parameters during the optimization, NAOS-SiO𝑥 combining with 50 nm-thick doped p+ a-SiO𝑥 :H fingers are applied on the p+ diffused surface and 100 nm-thick n+a-SiO𝑥 :H on the rear side. A annealing step is performed for the crystallization. A 20 nm-thick Al2O3 followed by a 75 nm SiN𝑥 layer are deposited on the front side and 100 nm SiN𝑥 layer is applied on the rear side. Lithography, wet chemical etch-back together with Al/Ag(front/rear) evaporation are utilized for solar cells metallization. The fabricated c-Si solar cells with poly-SiO𝑥 fingers has a champion efficiency with an efficiency of 7.91 %, with a 𝑖𝑉𝑜𝑐 of 562 𝑚𝑉, 𝑖𝑛𝑡 𝐽𝑠𝑐 of 34.7 𝑚𝐴 𝑐𝑚2 and fill factor of 40.5 %. The limited performance originates from the poor passivation in the poly-SiO𝑥 local contact area and severe 𝑖𝑉𝑜𝑐 drop after the metallization process. For further improvement, good performing c-Si solar cells by minimizing the recombination in the poly-SiO𝑥 local fingers contacts area and optimizing metallization steps are expected to be fabricated .

An increasing penetration of renewable energy sources in the global energy market necessitates an increasing amount of energy storage. Batteries are an excellent source of short term storage, used in vehicles, home storage and mobile applications. However modern technologies such as Li-ion batteries face resource scarcity and hence introduce geopolitical dependence. To this end Si-air batteries were recently, in 2009, explored in an attempt to devise a battery with high energy density and abundant materials.
The Si-air battery makes use of a silicon anode and an porous carbon cathode, to allow the circulation of air into the battery. Two electrolytes have been looked at in the past, KOH and the Room Temperature Ionic Liquid (RTIL) EMIm(HF)2.3F. The Si-air battery has excellent energy density in theory, with volumetric density being theoretically as high as 1 · 104 Wh/L. However, this theoretical energy density is as of yet far from reached, current research uses electrolytes which have a parasitic corrosion reaction with the silicon anode. This work aims to explore the usage of a new RTIL, BMPyr[NTf2], as the electrolyte in this battery. This RTIL has seen usage in Zn-air batteries, however it is yet untested for Si-air. The objective is to determine the discharge characteristics for a Si-air battery using this RTIL through comparison with KOH, with focus on the conductivity.
To do so first the relationship between conductivity and discharge potential for KOH was determined experimentally. The result found is that the discharge potential using KOH decreases with decreasing conductivity, however, this decrease is much larger than what can be solely attributed to the conductivity. Next the chosen RTIL BMPyr[NTf2], having a conductivity of 2.2 mS/cm at room temperature in a pristine state, was used in the battery discharges, where it was established to have an OCP of 0.7-0.8 V. From measurements no detectable consumption of Si was found after 1 hour of OCP. Further during the discharges it was found that the potential drops rapidly when discharge current is equal or greater to 2.5 μA. In an attempt to decrease the resistance in the battery cell a new design was created where the distance between the two electrodes is
decreased from 2 cm to 0.8 cm, using this second design a maximum OCP of 1.1 V was measured.
Finally by mixing in 1wt% and 3wt% water into the RTIL two mixtures are obtained with conductivity of 2.6 mS/Cm and 3.0 mS/cm at room temperature. Discharging these two mixtures at 20 nA, 100 nA, 500 nA and 2.5 μA it was found that for the 1 wt% the highest potential was found for 20 nA at 0.8 V. Meanwhile for the 3 wt% mixture the 20 nA discharge exhibited significantly lower potential at 0.4 V. For the 100 nA, 500 nA and 2.5 μA increasing conductivity led to increased potential, however similar to the KOH experiment, this difference in potential is larger than what is to be expected from purely conductivity changes. Finally, reproducibility of these experiments is low as a series of discharges with the same materials and current showed different potentials. These results combined lead to the conclusion of this work, thatthe relationship between conductivity and potential for the RTIL BMPyr[NTf2] is inconclusive, there are unknown factors influencing the discharge potential.

Global warming represents the most significant threat to humankind, making the need for renewable energy more crucial than ever. However, in densely populated areas near the coast, electricity production faces competition from various sectors such as agriculture, housing, and tourism. To address this challenge, one viable solution is to explore offshore electricity production.

Building upon this context, this research delves into investigating the wave-induced effect on power mismatch losses along a PV string in offshore floating photovoltaic (OFPV) systems. OFPV offers a promising solution for generating electricity in unused marine areas, complementing offshore wind energy. Although OFPV holds great potential, our understanding of its complexities remains limited, particularly regarding the impact of wave-induced power mismatch losses. To bridge this knowledge gap, a comprehensive approach is taken. A floating structure is modeled using the Bernoulli-Euler beam theory, while the fluid domain is analyzed using potential flow/linear wave theory. Structural behavior is examined in the frequency domain through the application of a FEM with the package Gridap in Julia. The wave amplitude spectra are determined using the Jonswap sea spectrum, with consideration given to four distinct sea states based on the Douglas sea scale: slight, moderate, rough and very rough. The optoelectrical modeling is conducted in pvlib in Python.

The results reveal that monthly energy losses due to power mismatch are negligible during summer months for all sea states studied. However, in winter months, monthly energy losses exceed 1%, with daily losses reaching up to 6%. Additionally, the orientation of the PV string is identified as a crucial parameter for minimizing losses. Finally, the findings indicate that using either a thick structure with a stiff and dense or a thin structure with a flexible and lightweight material can help reduce energy losses caused by power mismatch.

Technological advances, cost reduction, depletion of fossil fuels, environmental concerns, and growing energy demand are expanding photovoltaic solar energy (PV) in more latitudes and locations. A simple and effective procedure to assess the PV potential of a particular region is to analyse its climatic conditions. In general, climatic studies use the K¨oppen-Geiger (KG) climate classification as a reference. However, KG is solely based on temperature and precipitation, resulting in an unsatisfactory scheme for analyses in the PV field, since the most important variable, solar irradiation, is not considered. Thus, in 2019 Ascencio-V´asquez et al. developed a new worldwide classification based on temperature, precipitation, and solar irradiation: the K¨oppen-Geiger-Photovoltaic (KGPV) climate classification. Even though KGPV is a good improvement, it just consists of a simplified version of the KG groups subdivided into four levels of irradiation: low, medium, high, and very high. Hence, the climate parameters are not considered in a combined manner in the sorting process.

In this project, a new worldwide climate classification directly applicable to PV has been developed. Machine Learning proved to be a convenient tool to achieve this objective. First, supervised learning served to identify and assess the climate variables more correlated to the specific energy yield. More specifically, a Linear Regression model was implemented. Subsequently, these variables were used to create the classification by applying k-means, a clustering algorithm. The classification was optimised following a comprehensive qualitative analysis, resulting in a scheme based on seven climate variables and 20 clusters. By contrast, KGPV considers five variables. Even though it contemplates 24 groups at first, half of them are neglected based on a land-surface ratio and population density criterion, resulting in a classification based on 12 clusters. Hence, the methodology proposed in this work enables identifying new relevant regions. Moreover, “Machine Learning driven PV-climate classification” presents a satisfactory correlation with the specific energy yield, except for very low values, where the correlation is minor.

Lastly, the relationship between climate and degradation rate was explored. The complexity and non-linear behaviour of degradation demand an alternative approach. Random Forests was proposed, but it showed poor performance. It is necessary to be able to predict non-linearities and, at the same time, keep a logical mathematical relation between the supervised and clustering algorithms. In this regard, Multivariate Adaptive Regression Spline (MARS) might be a promising option.

Several promising photovoltaic (PV) concepts are supported by transistors. Along with the growth of PV capacity in the urban environment, issues related to partial shading highlight the interest in more shade-tolerant PV systems. An example of technologies improving a PV module’s energy yield under partial shading is the submodule power optimizer, including a power converter that operates sub-module maximum power point tracking (MPPT). Alternately, reconfigurable PV modules enable dynamic reconfiguration of the solar cells’ interconnections to optimize the energy yield depending on the irradiance distribution. Both technologies make use of transistors as fundamental components. Integrating the latter into the solar cell wafer might be a solution for cost reduction and reliability improvement and thus support such concepts. Moreover, that kind of transistor integration can have applications in solar cell-embedded electronic and digital devices.

In this thesis, a lateral metal-oxide-semiconductor field-effect transistor (MOSFET) and an interdigitated back-contacted (IBC) solar cell are integrated into the same crystalline silicon (c-Si) wafer. A combined process flow is developed to manufacture both components with a minimum number of additional steps compared to single-component manufacturing processes. One criterion for this is a high similarity in the design of the device. Therefore, a tunneling oxide passivated contact (TOPCon) solar cell structure is used, involving polycrystalline silicon (poly-Si) at the device’s backside. Similarly, the MOSFET’s gate is made of a highly doped poy-Si film. Ion implantation is used as a common doping process.

Both solar cells and transistors that were manufactured with the combined process flow are first characterized separately. The highest efficiencies obtained for n-type and p-type solar cells are 20.29% and 20.66%, respectively. This is achieved thanks to multiple combined passivation approaches including TOPCon, wet poly-Si etching, a front-side hydrogenated amorphous silicon (a-Si:H) film, and hydrogenated silicon nitride on both sides of the device. Different MOSFET layouts are explored to make the device able to handle relatively large currents. It is found that introducing several drain-source pairs in parallel is more efficient than increasing the channel width to reduce the on-resistance. The on-resistance is further minimized with a gate length reduction and wet chemical poly-Si etching. As expected, the comparison of PMOS and NMOS (MOSFETs built on n-type and p-type wafers, respectively) shows better on-performance for the latter. A minimum on-resistance value of 1 Ω is then obtained. However, a higher leakage current consistently seems to come along with reduced on-resistance; i.e., higher on-performance is coupled with lower off-performance. Finally, experiments are performed combining both components. Under illumination, the MOSFET exhibits lower off-performance due to the photovoltaic effect. However, this effect does not affect the on-performance of the component. The monolithically connected components exhibit I-V characteristics that depend on the applied MOSFET’s gate potential. In the on-mode, the solar cell maintains more than 95% of the conversion efficiency compared to the efficiency measured with the same solar cell without the transistor. However, a non-zero current is obtained in the off-mode, exhibiting low transistor blocking capability. Nevertheless, the large difference in characteristics obtained between the on- and off-modes proves the feasibility of integrating a solar cell and a transistor on the same substrate with a minimum number of additional processing
steps.

Silicon heterojunction (SHJ) solar cells are one of the most promising PV technologies nowadays due to high photoconversion efficiencies and low manufacturing costs. However, standard front/back-contacted (FBC) solar cells feature a front metal grid that brings shading to the front side of the devices, which limits the conversion efficiency of solar cells. One solution is to move metal contacts fully to the back by introducing interdigitated-back-contacted (IBC) architecture. In 2018, IBC-SHJ solar cells achieved a photoconversion efficiency of 26.7% holding a record for single-junction c-Si cells. However, the standard fabrication process of IBC solar cells comes with increased complexity and manufacturing costs. The focus of this research is on developing and optimizing a simple and industry-appealing fabrication process for high-efficiency IBC-SHJ solar cells.

The first part of the project investigates the simple processing of IBC-SHJ solar cells featuring tunneling recombination junction (TRJ). The first tunneling IBC devices are fabricated successfully. However, shunting is observed from the J-V curves of fabricated devices, which can be related to the internal shunting of tunneling IBC architecture and high lateral conductivity of p-type nc-Si:H-based blanket layer. Hence, alternative contact stacks are designed for application in the previously developed flowchart with the aim to minimize the lateral conductivity of the blanket layer and keep the fabrication process simple.

The proposed hole collection contact stack is firstly implemented in the front junction (FJ) FBC solar cells. The FJ FBC devices reach Voc of 704 mV and FF of 79.29% . Rear junction (RJ) FBC solar cells are fabricated featuring a novel electron collection contact stack that is developed within this thesis. Voc of 715 mV and FF of 82.24% are obtained in RJ devices. The results of RJ FBC solar cells with a newly developed contact stack show excellent results in terms of FF, making it a promising candidate for further application in IBC devices. The introduction of the optimized device design enabled the successful fabrication of IBC solar cells with the simple process developed for tunneling IBC devices while ensuring no shunting occurs. Fabricated devices represent a proof-of-concept of the novel configuration, providing a promising starting point for future development.

To extend Moore’s law, silicon carbide devices attend the researcher’s attention due to their irreplaceable advantages such as high critical breakdown electrical field, wide bandgap and excellent thermal conductivity without sacrificing too much charge carrier mobility. However, the defects on the SiC-oxide interface degrades the performance of the device and even get worse at high temperature, such as the threshold voltage shifting problems, limiting the design of the integrated circuits. The thesis models, characterise, analyses, measures and extracts the traps of SiC MOSCAP, to understand the trapped charge transportation and unreliability mechanism under high temperature.
Effectively using SiC materials necessitates the need to understand the physical properties itself. Due to the large bandgap, the inversion layer cannot be observable in low frequency C-V measurement. The electrical field, space charge region, surface potential and C-V curve in SiC devices all differ from Si devices. More importantly, the trapped charges fluctuate the surface potential of the SiC devices. To give insight into the mechanism governing the trapped charges, the mathematical solution of the trapped charges in the whole bandgap is solved.
To be specific, the trap behaviour at a single energy level is then followed. A nonzero transient current is generated due only to the capture and release of the trapped charges when the equilibrium condition is broken. The trapped charges with high energy are thermalized and an equivalent admittance is obtained which further be split into a capacitance and a conductance.
Rising temperature activates the dopant atoms that are not ionised, and the Fermi level shifts towards the midband. The variation of equivalent circuit components and physical parameters responds to the temperature. High temperature expands the SiC crystal and the trapped charges are easy to receive energy from phonons so that the interaction between traps and the conduction band is enhanced and more empty states are waiting for the recombination of the charge carriers.

To further improve the light management and optical performance of solar cells, research into nano-textured interfaces has led to a need for a fast and accurate wave optics model. Currently, within the PVMD group at the TU Delft an optical solar cell simulation tool, GenPro4, is being developed to allow for the quick optimization and analysis of solar cell designs. However, the implemented wave optics model has limited accuracy and thus an alternative model is sought.

In this thesis, we researched several rigorous wave optics simulation methods such as: finite element method, finite difference time domain, transfer matrix method, and rigorous coupled wave analysis. Based on three decision criteria (speed, accuracy, and compatibility) the choice of implementing rigorous coupled wave analysis (RCWA) was made. Besides the standard RCWA formulations, a few improvements were made. S-matrices were used to increase
speed and memory efficiency of the program. Furthermore, calculation of the local E-field allowed for the determination of absorption per material in our cell. Lastly, an angular intensity distribution, known as scatter matrix, was produced as output to allow for the full integration with GenPro4.

We validated our new model by comparing results of a nano-textured GICS solar cell with previously conducted finite element method (FEM) simulations. Over a large wavelength range our model showed good agreement with the FEM data. However, slight inaccuracies were observed at longer wavelengths (>1000 nm) as simulation of the metal back reflector became infeasible. Highly absorbing materials, such as metals, potentially required several hundred Fourier modes to be modeled accurately. However, simulations with such a high number of Fourier modes is not feasible as the computer resources (RAM) and computational time
needed grow exponentially. Furthermore, for very small textures, RCWA converges with the GenPro4 flat model as is expected for sufficiently small textures.

Nevertheless, integration of RCWA with GenPro4 was achieved. To demonstrate the ability to quickly and easily simulate real work cell designs, a case study of a perovskite/silicon tandem cell was conducted. In the case study, a combination of 16 interface mythologies was simulated and compared. With the optimal combination showing a potential improvement of 2% over the reference cell.

Renewable energy sources such as solar and wind energy rely on climate­ and weather conditions, like sun irradiation in the case of solar energy, and wind speed in the case of wind energy. These change throughout the day and with the seasons. There are periods of little wind, and during the night there is no sunlight. During periods of no sunlight and little to no wind, there is still a demand for energy. This leads to a shortage of energy. On the other hand, there are periods when the amount of available wind­ and solar energy will surpass the demand for energy, leading to an energy excess. To mitigate this mismatch between energy production and energy demand the excess energy can be stored to be used during periods of shortage. Many different solutions for this have been investigated in recent years. One of the storage technologies that is currently quite dominant is battery storage. Lithium-ion batteries are used quite widely, among others in battery electric vehicles. However, the use of batteries as a storage device to overcome energy mismatch is not yet implemented on a large scale, as most battery technologies are still quite novel, making them
uneconomical for this use compared to traditional hydrocarbon fired power plants. Furthermore, many battery technologies depend on scarce and expensive minerals. Recently, a battery utilizing silicon as its anode and oxygen from the air at the cathode has been proposed. This so­called silicon­-air battery utilizes mainly silicon and oxygen, which are the two most common elements on earth. Furthermore, the theoretical energy density of this battery type was shown to be significantly higher than the energy density of lithium­-ion batteries. Because of this, the silicon­-air battery has been a growing area of research in the last years.

Battery models help to simulate batteries based on empirical data and electrochemical systems. These models are a powerful tool in the evaluation of the performance of batteries. Parameters of the battery can be altered quickly and specifically. This can provide a powerful analysis tool to determine weaknesses in a batteries. They can also help in further developing an understanding of the operating principles of the battery technology. A specific type of model is the finite element model. In this type of model the object that is modeled is divided into small pieces and for each piece a set of (partial) differential equations is evaluated. Different electrochemical, chemical, physical and mathematical models can be modelled and combined in this tool. For this thesis a finite element model of an alkaline silicon­-air battery is developed in COMSOL. The model is based on an earlier model that was developed in 2020.

Besides the discharge mechanism, alkaline silicon-­air batteries are subject to two secondary reactions that hinder the performance of the battery: corrosion and passivation. Corrosion consumes a large part of the silicon without contributing to the discharge. Passivation creates an oxide layer on the surface of the silicon electrode, stopping the discharge reaction. Both these reactions have been implemented in the model. Besides that, a metal contact on the silicon anode is implemented in the model. The parameters used in this model are supported by empirical values for these parameters. Finally, the model was compared to experimental results.

The simulation of the discharge of the alkaline silicon­air battery was improved in several ways compared to the pre-­existing model. The corrosion was shown in the simulations, although the mechanism is somewhat simplified because of the 1D nature of the model. The passivation reaction was shown in the simulations as well, and was improved on compared to the previous model by breaking it up into two steps. Using this model, experimentally observed trends could be simulated reasonably well. The simulated discharge potential was a close representation of the experimental data, although the open circuit potential was somewhat higher, and for higher current densities the potential was somewhat lower. For different electrolyte concentrations the model showed results similar to what was found in experiments.

Renewable energy sources (RES) such as Solar and Wind energy rely on the availability of natural resources like sunlight in the case of Solar and wind speed in the case of Wind energy generation which is variable in nature. There are periods where there is excess energy production than needed and periods of energy shortage where not enough energy is produced to meet the demand. To mitigate this mismatch, a short term solution is to use batteries in order to store energy at times where energy production is more than the energy demand. This stored energy would be later used at times where energy production is low and meet the energy demand. However, the current battery technology is still novel for this application making it uneconomical when compared to current energy infrastructure of using power plants. The current battery market is held by Li-ion batteries which uses lithium as a raw material which is a rare earth material. In 2009, a battery cell utilizing Si as its anode and air as its cathode was discovered. As this system relies on two of the most abundant elements in the earth's crust which is silicon and oxygen and has much higher theoretical energy density than Li-ion batteries, it has become a growing area of research and development. Battery models are created to simulate battery operations based on empirical formulas and electrochemical reactions taking place in the battery. Development of these models are very critical as they provide results and optimum condition evaluations much faster than physical testing with minimal resources. A battery model for the alkaline Si-air battery which utilizes KOH as the cell electrolyte is developed in Simscape (MATLAB) as part of this thesis. The modelling parameters are also subjected various physical conditions such as varying electrolyte concentration and change in electrode materials and the variation is investigated for model validation to study whether changing physical conditions of the Si-air cell has an effect on the modelling cell parameters. It is supported with experimental results obtained from discharging a fabricated Si-air cell. It was concluded that there are cell parameters which are dependent only on the state of charge (SOC) of the cell and one cell parameter that is a function of both the SOC as well as the discharge profile of the cell. The fabricated Si-air cell gives higher open-circuit potential (OCP) values than what was reported constant 1.4 V in literature which is speculated to be due to the usage of a 99% Aluminum and 1% Silicon (Al:Si) back contact layer. Average OCPs ranging from 1.5 V to 1.45 V which varies due to change in electrolyte (KOH) concentration is achieved. The MATLAB battery block is calibrated to be integrated with energy system models as a Si-air battery.

Photovoltaic (PV) system yield prediction models are an important topic in the field of PV solar energy. An accurate prediction model could not only be used for optimising the PV system design, but is also expected to realise the yield potential of innovative PV technologies. In the next generation of PV technologies, one of the most promising concepts is the tandem solar cells. In recent years, these cells have impressed the solar industry by their rapid growth of the maximum power conversion efficiency (PCE). Since tandem solar cells are still at the lab phase, their yield potential under realistic conditions are an interesting field of study as well. However, the existing yield prediction models are not yet available for these tandem cells. In order to fill this gap, a prediction model developed in the Photovoltaic Materials and Devices (PVMD) group of TU Delft, called the PVMD Toolbox, has been adapted to be compatible with the tandem solar cells. In this thesis project, the version 3 of the Toolbox was developed. First the PVMD Toolbox was improved. Except monofacial c-Si cells and bifacial c-Si cell, it is now also available for tandem cells. One of the most promising tandem concepts, the perovskite/c-Si tandem, was taken as a reference tandem configuration integrated in the Toolbox. The Toolbox was also modified to take the influence of solar spectra into consideration and analyses cell performances individually. Secondly, the accuracy of the Toolbox was validated. A new figure of merit called 'relative total deviation' is put forward in this report, which calculates the ratio between the sum of deviations that each simulation introduces, and the total measured energy yield. When the electrical parameters were taken from the own measurements, the relative total deviation of simulation results was only 8.6%. Finally, the Toolbox was applied to two case studies. In the first study, it was found that the annual energy yield (AEY) of perovskite tandems can be increased up to 0.4% by optimising perovskite thickness for a certain location. The second case study compared the AEY of the tandem module and conventional c-Si module. Perovskite tandem module showed a high AEY, around 36% higher than that of the c-Si module. However, perovskite tandem had a lower specific yield as they are more sensitive to the spectral variation

Multi-junction solar cells with Si alloys have true potential for high conversion efficiency, because of the spectrum splitting capability. For optimal spectral utilization, a multi-junction silicon based device needs a silicon alloy with a bandgap between that of nc-Si (1.1 eV) and a-Si (1.8 eV). a-SiGe:H has a tunable bandgap between 1.4-1.6 eV by varying the GeH4 flow rate in the layer. An investigation of deposition parameters on PECVD processed a-SiGe:H films showed that variation of the GeH4/SiH4 flow rate is the most influential deposition parameter to achieve bandgap tuning. It influences the optical-, electrical- and material properties due to the fact that it directly changes the GeH4 flow rate in the material. Subsequently, a n-i-p substrate single junction a-SiGe:H solar cell is fabricated. This is the reversed p-i-n superstrate a-SiGe:H solar cell, fabricated by the PVMD group. It has a Voc of 508 mV, a FF of 0.39, a Jsc of 9.9 mA/cm2 and a final efficiency of 2.9%. Due to the low performance, manipulation techniques were introduced. The different proposed shapes consist of bandgap grading in the absorber through GeH4 flow rate profiling. A study on buffer type and thickness, different profiling schemes, grading widths and total absorber thickness strongly improved the device performance. The overall champion single junction a-SiGe:H solar cell has a 3.2 nm n/i i-a-Si buffer combined with a 5 nm n/i i-a-SiGe:H buffer, a V-shape GeH4 peak flow rate of 2.4 sccm, a 134 nm n/i grading width, a 36 nm i/p grading width and a total absorber thickness of 170 nm. This cell generates a Voc of 735 mV, a FF of 0.64, a Jsc of 13.23 mA/cm2 and a final efficiency of 6.18%. This is a relative increase of 113.8% in efficiency. The single junction solar cell fabrication is followed by demonstration of a two-junction device. The overall champion tandem solar cell consists of a 200 nm a-Si:H top cell and a 170 nm a-SiGe:H bottom cell with a V-shape GeH4 peak flow rate of 5.3 sccm. This champion tandem solar cell generates a Voc of 1395 mV, a FF of 0.69, a current limiting Jsc of 8.34 mA/cm2 and a final efficiency of 7.99%. Finally, research proved that the change in top and bottom cell thickness, the maximum GeH4 flow rate and the U- and V-shape profiles are interesting manipulation techniques in a multi-junction device due to their flexibility to increase the current limiting Jsc and improve current matching.

The use of renewable energies has been growing in a considerable way in the world. Until 2017, 18% of European Union’s total installed power generation capacity was wind power capacity. The level of grid penetration of wind turbines has also increased significantly in the Netherlands. This high level of penetration of wind energy affects the behavior of the system during an event (such as a short circuit), which is not the same that with only conventional generation in the system. The level of detail in the dynamic network model of a transmission system becomes of great importance when a big amount of wind energy is connected to the electrical system. In the current dynamic model of the Netherlands transmission system, negative load is used to represent wind turbines, however, this could be no longer sufficient if more wind turbines are connected to the grid.
The purpose of this Master Thesis Project is the study and analysis of voltage response of wind turbines models based on the IEC 61400-27-1 standard and the WECCWind Plant DynamicModeling Guidelines, both of them currently implemented in several softwares.
This project proposes a modelling methodology for distributed wind turbines, using a single turbine representation and a combined model instead of a negative load directly connected to the grid.
PowerFactory and PSSE softwares are used for the modelling of wind turbines, allowing to compare the models based on the IEC standard and the models based on the WECC guidelines respectively.
For the simulations performed in these two softwares, parameters suitable for comparing both of them are proposed. Besides, an analysis on the differences between both models is provided.
The parameters proposed are used later on for the modelling of distributed wind turbines in the grid.
The methodology for the modelling of distributed wind turbines was proposed and analysed using a region in the Netherlands as case of study and the PSSE software (widely used by transmission system operators) with the generic parameters proposed in the previous analysis.
The proposed methodology and parameters show a more realistic behavior of the wind turbines compared to the use of a negative load. It also provides a grouping proposal depending on the types of distributed wind turbines connected to the grid. In some cases, when the wind energy connected to the system has low impact, the use of a detailed model instead of a negative load is not very representative. Therefore, this project proposes a calculation for the impact that wind energy has in each substation, making easier to decide what is the most suitable level of modelling detail.

Efficiency improvements of solar cells, growth in photovoltaic cells manufacturing, and declining prices of solar modules are just a few of the factors that have allowed solar power to break records (320 GW) in global cumulative installed capacity in 2016. In the energy systems of the future, solar energy will be the predominant energy source. However, the growth in solar power brings new technical challenges to overcome.
Power intermittency, grid flexibility, and surplus electricity are just a few of the challenges that must be addressed for the power systems of the future.
In the light of these challenges, this thesis provides new insights in the use of solar energy to produce hydrogen via a PEM electrolyzer. In order to achieve this goal, a hybrid power system model of hydrogen production using solar power was developed. The system consists of a PV array, a battery bank, a PEM electrolyzer, hydrogen tank, and a power control unit.
The results are structured in two parts. First, simulations of three configurations between the panel and the electrolyzer: (i) direct coupling, (ii) including an MPPT, and (iii) including a battery. Second, simulations of several component sizes of PV modules, battery bank, and electrolyzer stack. These simulations were analyzed for yearly irradiance data from Delft.
An analysis of energy yields, hydrogen production, system efficiency, and the impact on the electrolyzer lifetime, is performed for each of the configurations.
Additionally, Wawa, a lab-scale solar-to-hydrogen system has been designed, built and tested. Wawa provides a practical hands-on understanding the hydrogen production via PEM electrolysis using solar power.
Based on the simulation results, it is clear that the lifetime of the electrolyzer can be positively affected by including a battery as an energy buffer. An additional conclusion is that the shape of the irradiance curve plays an important role when sizing the components of the system.
Hopefully, this research will motivate students to address more research on how solar-to-hydrogen systems can help to develop the power systems of the future.

The transportation industry is causing 14% of the worldwide greenhouse gas emission. Therefore, the United Nation concluded with the Paris climate agreement to reduce and limit their emissions to keep the global average temperature increase below 2 degrees Celsius. Based on the agreement the European union introduced new regulations to limit the average fleet emission of car companies. In this push towards lowering emission the companies introduced their first generations of electric cars. To further improve the efficiency of the electric drive train new multilevel topologies were introduced. One of the topologies is called modular multilevel converter (MMC) introduced by R. Marquardt and A. Llesnicar in 2003. This new topology main advantage are its modularity and the option to use low voltage component. However, no company industrialized the MMC for drive train application. The reason therefore are the extensive control architecture, hardware and software wise. This thesis investigated possible ways to reduce the wiring and complexity by introducing a low level communication bus together with distributing the control to remove the centralized architecture. Therefore, the different possible low level communication bus were analysed and compared. The different bus protocols were compared based on speed and time to send the same amount of information to control a MMC. It was concluded that the serial peripheral interface bus (SPI) shows the highest capability for the proposed single phase 5 level converter set-up. Therefore, an experimental system was built to validate the performance. The system itself was designed with the goal to use low cost and low voltage component. The validation of the experimental set-up showed the stable operation of the system with an open loop control. Thereby it proofs the possibility to integrate and control the MMC with a low level communication bus. The results can be used as a baseline to further research on integrating theMMC and make it viable for drive train applications.

In this thesis, graded bandgap energy a-SiO_x:H solar cells are developed to attain a high JSC without compromising their high V_OC × FF product. First, a grading method which takes into account the interdependence of bandgap energy, deposition rate and the desired grading profile for a-SiO_x:H materials is developed. Then, graded bandgap energy a-SiO_x:H solar cells are fabricated to investigate the optimum grading width. The bandgap energy is linearly graded from 2.1 eV to 1.96 eV. It was observed that, when fabricating graded bandgap energy a-SiO_x:H solar cells, the grading width at both the ends of the absorber layer should be as small as possible. A 10-nm thick grading at the front end and 20-nm thick grading in the rear of the absorber layer showed the best result among all the graded bandgap cells developed during the optimization, with an efficiency of 8.2 % (V_OC : 0.96 V, J_SC : 13.36 mA/cm2, FF: 0.64).

The effects of grading the bandgap energy on the performance of a-SiO_x:H solar cells were also investigated. For instance the bandgap variation within the graded region was investigated. We found that increasing the range over which the bandgap energy is varied within a fixed graded region was detrimental to the J_SC and FF. When increasing the thickness of the graded bandgap energy absorber layer for a-SiOx:H, J_SC as high as 14.4 mA/cm2 was achieved. Also, the increase in the thickness of these graded bandgap energy absorber layers did not result in a drastic drop in efficiency as seen for a-SiOx:H solar cells without bandgap energy grading.

Finally, optical simulations of graded bandgap energy a-SiO_x:H solar cells were attempted. Graded bandgap energy i-a-SiO_x:H layers were simulated. The matching of the simulated absorbance to the measured absorbance of the graded bandgap absorber layers were found to be satisfactory. However, the simulations of the graded bandgap energy a-SiO_x:H solar cells were not satisfactory and requires more attention.

Further research into improving the FF of graded bandgap energy solar cells can help increase the VOC × FF product and efficiency of such devices. Moreover, the increase in J_SC obtained by grading the bandgap energy makes the device a suitable candidate for a top cell in four-terminal (4T) applications.

In the transition towards a renewable based energy supply, one of the main challenges is the intermittent nature of most renewable energy sources. In order to ensure a stable energy supply, different storage technologies attract a lot of research attention. For long term storage, using hydrogen as artificial fuel is a promising option. However, in order for hydrogen storage to be renewable, the hydrogen must be produced using renewable energy. A possible option is to use solar energy to drive the electrolysis of water. In this way, hydrogen is produced directly from sunlight by driving the redox reaction with a reversible potential of 1.23 V. However, due to overpotentials and possible losses a voltage of 1.6-2 V is needed form the used device to drive the reaction. Recently, a wafer based triple junction silicon solar cell was proposed to generate the voltage needed to drive the water splitting reaction. The cell uses an n-type crystalline silicon wafer as substrate, and has an a-Si/nc-Si/c-Si structure. Although this cell demonstrates the feasibility of this technology, the performance is not good enough yet to drive the water splitting reaction efficiently.
In this work, several ways to optimize the triple junction solar cell have been studied. First, optimising the tunnel recombination junctions improves the open circuit voltage of the device. For the tunnel recombination junction between the top a-Si and the middle nc-Si cell, this is done by using a combination of a thin n-SiOx layer and a thin n-a-Si layer. Apart from a small improvement in optical performance this configuration improves the conductivity of the junction and also slightly enhances charge separation and collection in both sub-cells. For the junction between the middle nc-Si and the bottom c-Si cell, the same result was achieved by increasing the doping in the n-layer. Subsequently, to improve current matching of the device, the nc-Si layer thickness can be increased to 3500 nm without sacrificing the electrical performance. In addition, optimizing the interface between the top p-nc-SiOx layer and the front transparent conductive oxide (TCO) also improves the electrical performance of the device. Moreover, it was found that using hydrogenated indium oxide as front TCO instead of indium doped tin oxide increases the current by decreasing the reflection in the wavelength region of the current limiting nc-Si middle cell by having reflection, and also increases the open circuit voltage of the device by 0.3 Volts. The final triple junction cell achieved an open circuit voltage of 1.93 V and a short circuit current density of 8.5 mA/cm2, with a fill factor of 0.65. With these improvements, it is estimated that a solar to hydrogen efficiency of 6.2 % can be reached by using an IrOx counter electrode.